// var num = 123  // new Number(123)
// //原始类型一定不能添加属性和方法，属性和方法是对象独有的
// num.a = 'aaa'
// delete num.a
// console.log(num.a) //undefined
// console.log(num) //123

var num = new Number(123)
console.log(num + 1) //124

var num = new Number(123)
num.a = 'aaa'
console.log(num.a) //aaa
